1. Field of the Invention
The invention relates to a combustion control system typically used with a combustion apparatus such as a boiler, a heater or the like. More particularly, the combustion control system of this invention includes a remotely actuated, linkage strut adjustor apparatus for trim adjustment to the air to fuel ratio of a combustion apparatus. The linkage strut adjustor also protects the control system against mechanical overload damage.
2. Description of the Prior Art
It is known to mechanically connect the valves controlling fuel feed and air intake in order to establish a definite and selectable air to fuel or oxygen to fuel ratio. The simplest and least expensive combustion control system is known as the "jackshaft" or "single-point" positioning system. This system consists of a mechanical linkage arrangement in which a master arm is connected to a main shaft for controlling the fuel valves and a slave arm is connected to the air damper and is responsive to the main shaft through an intermediate linkage strut. Such a mechanical arrangement establishes a master-slave relationship between the fuel and air adjustment devices. The intermediate linkage strut of the prior art system is adjusted, as a result of calibration, to provide a fuel to air ratio which remains unchanged through all load requirements of the combustion apparatus.
However, in order to maximize combustion process efficiency through various load requirements, changes in the BTU value of the fuel, viscosity of the fuel, combustion air temperature, burner clogging, etc., the original, calibrated relationship between fuel and air must be adjusted. Such an adjustment is often referred to as an oxygen trim adjustment and may be necessary several times a day. While such adjustments can be effected by changing the interconnecting points at the opposite ends of the linkage strut, this approach is obviously time consuming and necessitates a recalibration of the jackshaft positioning system.
It is taught in U.S. Pat. No. 4,249,886, which patent is assigned to the assignee of the present application, that an angularly modifiable trim link can be incorporated into a conventional jackshaft positioning system. The trim link allows the conventional master-slave relationship between the fuel control and damper control means to continue. In addition to this relationship, the trim link effects slight adjustments to the damper means in order to better regulate the air-fuel ratio. The specific articulation of the trim link is controlled by a trim positioner means which is responsive to a combustion products analyzing device.
Another control system for a combustion apparatus is taught in U.S. Pat. No. 4,264,297 in which both the length of one of the arms in the master-slave relationship and the length of the intermediate link are adjusted as a function of combustion products generated in the controlled combustion apparatus. The length changes are effected by a piston/cylinder assembly actuated by compressed air or hydraulic fluid or an adjustment screw rotated by an integral electric motor. However, compressed air is unavailable for most commercial applications of this type of control system, hydraulic fluid is dangerous and the space available in most jack shaft systems is not adequate to accommodate the diameter of a motor with sufficient power to adjust the link. The weight of the motor may be too great for support by small diameter links in a jack shaft system.
It is an object of this invention to provide a combustion control system adjustor apparatus which can be readily installed in a conventional jackshaft combustion control system. The adjustor apparatus is a remotely actuated, intermediate linkage strut adjustor which requires a mininum of physical space for installation and operation.
It is also an object of this invention to provide a reliable linkage strut adjustor with a mechanical overload protection means which protects both the linkage strut adjustor and the intermediate linkage strut from damage during jackshaft positioning.